The present invention relates to a process for separating products contained in an alkyl hydroperoxide cleavage mass, and in particular, to a process for the removal of salts of neutralization present in a cleavage mass for the manufacture of phenol.
In general, phenol is manufactured by oxidizing an alkyl substituted aromatic compound, such as cumene, to form the hydroperoxide derivative thereof, followed by cleavage of the hydroperoxide with a mineral acid such as sulfuric acid to form a cumene hydroperoxide cleavage mass. The cleavage mass generally contains species such as phenol, acetone, xcex1-methyl styrene (AMS), cumene, cumyl phenol (CP), dimethylbenzyl alcohol (DMBA), acetophenone (AP), AMS dimers (AMSd), tars and heavies, and mineral acid such as sulfuric acid. Prior to separating out the different species and recovering acetone and phenol, the cleavage mass is neutralized with a caustic, such as sodium hydroxide, to prevent the acidic cleavage mass from corroding downstream equipment. Much of the salt is separated and removed from the process in a wash/phase separation step prior to feeding the partially or wholly neutralized cleavage mass to a splitter and further purification columns. However, a significant quantity of salt remains in the cleavage mass entering the splitter, and this quantity of salt becomes more concentrated as the stream passes from one purification column to the next.
In the course of making phenol, the fully or partially neutralized cleavage mass passes through several distillation and purification columns to ultimately form a stream of heavy by-products. The heavy by-product stream may be subject to cracking, and the bottoms of the cracker are usually incinerated. The heavy hydrocarbon by-product stream feeding a cracker or furnace, however, contains a high concentration of the salts of neutralization, typically sodium sulfate. The salts remaining after the wash/phase separation step are carried into the splitter, which separates out ketone as an overhead from phenol as a phenol bottoms stream, into the phenol bottoms stream and into further downstream equipment through the bottoms stream of each purification column, all the way to the cracker or furnace. It is in the cracker and furnace, and in the reboiler for the cracker, where the salts of neutralization settle and are no longer carried through. The settling of the salts in the cracker, reboiler, and furnaces causes operating problems, requiring intermittent shut down to clean the equipment or replace parts. The salts also degrade the value of a tarry mass as fuel for burning. Therefore, it is highly desirable to remove as much salt as possible prior to feeding a cracker or furnace.
Many methods have been proposed for removing salts of neutralization in the manufacture of phenol. One such method, disclosed in U.S. Pat. No. 4,328,377, involves feeding a neutralized cleavage mass to a multi-tray (20 or more) splitter, separating out the ketone as an overhead from a bottom fraction comprised of a crude phenol stream, and recovering the phenol, wherein a liquid layer located near or below the cleavage mass feed site but above the bottoms is withdrawn from the splitter column, phase separating the liquid layer into an oil layer and an aqueous layer containing the salts of neutralization, and recycling the oil layer back to the splitter column at a site below the liquid layer withdrawal site. To enhance the ability of the liquid layer to phase separate, a hydrocarbon having a lower boiling point than phenol and a specific gravity difference of at least 0.03 is added to the liquid layer.
A disadvantage of this process is that large quantities of liquid layer must be removed and processed to sufficiently reduce the amount of salt to the desired level. For example, for every 100 parts by weight per hour of cleavage mass fed to the mutli-tray splitter, 127 parts by weight per hour of a liquid sidedraw was processed in a phase separator. Treating such large amount of liquid requires adding and processing corresponding large quantities of water, and adding large quantities of lower specific gravity hydrocarbon, processing large amounts of oil layer, and increasing the volume of the phase separation vessel. It would be desirable to discharge the salts of neutralization from the process by feeding a phase separator with a small amount of hydrocarbon, discharging low amounts of water containing the salts of neutralization from the process while effectively removing at least 80% of the salts of neutralization from the process, using low amounts of lower density hydrocarbon to enhance phase separation, concentrating the salt in a purge stream discharged from a phase separator to high levels, and/or employing a smaller phase separation vessel It would also be desirable to employ a process for manufacturing phenol where the amount of water or lower density hydrocarbon lost from the process is minimized or eliminated
In one embodiment of the invention, there is provided a process for the manufacture of phenolic compounds comprising:
a) separating a neutralized aralkyl (aryl alkyl or alkyl aryl) hydroperoxide cleavage mass stream containing salts of neutralization into a crude ketone stream and a crude phenolic stream containing the salts of neutralization;
b) separating the crude phenolic stream into a concentrated phenolic-rich stream, enriched in phenolic compounds, and a crude phenolic bottoms stream enriched in tars and alpha methyl styrene dimers, each compared to the crude phenolic stream, said crude phenolic bottoms stream containing salts of neutralization;
c) to the crude phenolic bottoms stream, adding water and a diluent composition, thereby forming a phase separable crude phenolic bottoms stream, said diluent composition comprised of a hydrocarbon phase compatible with the crude phenolic bottoms stream and having a combined density lower than the density of the crude phenolic bottoms stream;
d) separating the separable crude phenolic bottoms stream into a hydrocarbon phase and an aqueous phase containing salts of neutralization;
whereby the amount of salts of neutralization in the hydrocarbon phase is reduced compared to the amount of salts of neutralization present prior to separation.
In another embodiment of the invention, there is provided a process for the manufacture of phenolic compounds comprising wholly or partially neutralizing an aralkyl hydroperoxide cleavage mass feed containing an acid and having a pH of less than 6 in neutralization zone, thereby forming an aqueous neutralized aralkyl hydroperoxide cleavage mass containing salts of neutralization, subsequently separating said aqueous neutralized aralkyl hydroperoxide cleavage mass into an aqueous stream and a neutralized aralkyl hydroperoxide cleavage mass stream containing a smaller amount of salts than in the aqueous stream, subsequently separating the aralkyl hydroperoxide cleavage mass into a crude ketone stream and a crude phenolic stream containing the salts, separating said crude acetone stream into a concentrated ketone rich stream and a crude ketone bottoms stream, separating said crude phenolic stream into a concentrated phenolic-rich stream and a crude phenolic bottoms stream, and ultimately separating from the crude phenolic bottoms stream a light ends stream and a tarry stream containing an amount of salts reduced by at least 90% of the amount of salts contained in the crude phenolic bottoms stream, and recycling at least a portion of said crude ketone bottoms stream and at least a portion of said light ends stream as feeds to said aralkyl hydroperoxide cleavage mass, said aqueous neutralized aralkyl hydroperoxide cleavage mass, or to both.
In yet another embodiment of the invention, there is provided a composition comprising at least 40 wt. % water, less than 20 wt. % phenolic compounds, alkali metal salts in an amount of at least 1.5 wt. %, phenolic tars, and xcex1-methyl styrene dimers, wherein the volume ratio of water to all ingredients in said composition other than water is between 1:1 to about 3:1.
In yet a further embodiment of the invention, there is provided a process for removing salts of neutralization present in a neutralized aralkyl hydroperoxide cleavage mass comprising removing 80 wt. % or more of said salts from said cleavage mass through one or more aqueous streams discharged and purged from said process, the combined flow rate of all aqueous purge stream(s) containing the salts being less than 5 parts by weight per hour based on a flow rate of 100 parts by weight per hour of the cleavage mass fed to a means for separating said cleavage mass into a crude ketone stream and a crude phenolic stream.
There is also provided an embodiment for manufacturing phenolic compounds comprising feeding a neutralized aralkyl hydroperoxide cleavage mass containing salts of neutralization to a splitter, separating acetone and phenol from said cleavage mass in the splitter, removing all or a portion of the phenol from the splitter, followed by feeding said all or a portion of said phenol to a phase separation vessel having a volume of 5000 gallons or less, based on 100 parts by weight per hour of cleavage mass feed to the splitter, and removing at least 80 wt. % of the salts of neutralization from said phenol.
In another embodiment, there is provided a process for removing salts of neutralization, comprising feeding an aralkyl hydroperoxide cleavage mass containing salts of neutralization to a splitter, separating acetone from a crude stream of phenol in said splitter, followed by feeding a portion or all of said crude phenol stream to a phase separator as a feed comprising hydrocarbons, water, and salts of neutralization, the total amount of hydrocarbon feed from any source to said separator being less than 10 parts by weight per hour, based on 100 parts by weight per hour of said cleavage mass fed to the splitter, wherein at least 80 wt. % of the salts of neutralization are removed from the crude phenol stream.
In another embodiment of the invention, there is provided a process for removing salts of neutralization from an aralkyl hydroperoxide cleavage mass containing salts of neutralization comprising separating acetone from said cleavage mass, followed by purging the salts of neutralization in an aqueous purge stream comprising at least 3 wt. % of the salts of neutralization and at least 90 wt. % water, based on the weight of the purge stream.
In a further embodiment of the invention, there is provided a process for making phenol comprising feeding an aralkyl hydroperoxide cleavage mass containing salts of neutralization into a splitter and separating the cleavage mass in the splitter into a ketone stream and a phenol stream containing the salts, optionally concentrating the phenol stream by further distillation, and forming a phase separable hydrocarbon stream from said phenol stream comprising adding a net amount of water of 5 parts by weight per hour or less to the phenol stream, based on 100 parts by weight per hour of cleavage mass fed to the splitter, phase separating the phase separable hydrocarbon stream into an aqueous stream and a hydrocarbon stream, and discharging a portion or all of the aqueous stream from the process as an aqueous purge stream, wherein at least 80 wt. % of the salts of neutralization present in the cleavage mass entering the splitter are removed through said purge stream.
The various features of the invention are described in further detail below.